Radiation sensitivity of megakaryocyte colony-forming cells in human placental and umbilical cord blood.

The in vitro radiation sensitivity of CFU-Meg isolated from human placental and umbilical cord blood was evaluated in plasma clot cultures stimulated by recombinant human cytokines, including thrombopoietin, the FLT3 ligand (FLT3LG), interleukin-3, interleukin-11 and stem cell factor. The CD34(+) cells were irradiated with X rays at a dose rate of 73 cGy/ min. The megakaryocyte colonies were identified by using an FITC-conjugated antibody to glycoprotein IIbIIIa and were classified into two groups based on colony size: large colonies (immature CFU-Meg) and small colonies (mature CFU-Meg). Treatment with thrombopoietin alone or in combination with FLT3LG and/or interleukin-11 gave exponential radiation survival curves (D(0) for immature CFU-Meg = 56-77 cGy, D(0) for mature CFU-Meg = 86 cGy-1.12 Gy), while marked shoulders were observed on the survival curves for colonies supported by the combination of thrombopoietin, interleukin-3 and stem cell factor (D(0) for immature CFU-Meg = 89- 98 cGy; D(0) for mature CFU-Meg = 1. 25-1.31 Gy). Our results showed that the immature CFU-Meg were more radiosensitive than the mature CFU-Meg and that the combination of cytokines, including thrombopoietin, interleukin-3 and stem cell factor, affected the radiation sensitivity of CFU-Meg to the same extent as with thrombopoietin alone or in combination with FLT3LG and/or interleukin-11.